Sen. Bernie Sanders, I-Vt., speaks about health care on Capitol Hill on June 26. Single-payer was a major policy plank of Sanders' 2016 presidential campaign.

Vermont Sen. Bernie Sanders will introduce a bill next month to create a government-run, single-payer health care system. And he knows it's going to fail.

"Look, I have no illusions that under a Republican Senate and a very right-wing House and an extremely right-wing president of the United States, that suddenly we're going to see a Medicare-for-all, single-payer passed," he said recently, sitting in his Senate office. "You're not going to see it. That's obvious."

The point of the bill, Sanders says, is to force a conversation: "Excuse me: why is the United States the only major country on earth not to guarantee health care to all people? Why are we spending far, far more per capita on health care than any other nation? Why do we pay the highest prices in the world for prescription drugs?"

Single-payer was a major policy plank of Sanders' 2016 presidential campaign, and he has been ready all year to put it into legislation. He was just waiting for Republicans to wrap up their effort to repeal and replace the Affordable Care Act, also known as Obamacare.

The measure is the latest example of how Sanders is trying to push the Democratic Party — a party he is not formally a member of as an independent — to the left.

Sanders and his staff are confident a substantial number of Democratic senators will co-sponsor the measure. But many Democratic Party leaders continue to hold the idea of single-payer at arm's-length. Democratic National Committee Chairman Tom Perez regularly pivots to a broader answer about health care policy when he is asked whether he backs a single-payer plan.

"We believe that health care is a right for all, and not a privilege for a few," Perez recently told NPR. "And right now, in Washington, D.C., in the political climate in which we live, preserving the Affordable Care Act is a major victory."

House Minority Leader Nancy Pelosi was more direct earlier this year when she was asked whether Democrats should run on a single-payer platform in 2018.

"No," Pelosi said. "I say to people, 'You want to do that, do it in your states.' "

"The comfort level with a broader base of the American people is not there yet. Doesn't mean it couldn't be. States are a good place to start," she added.

Democrats in Pelosi's home state of California tried to pass a single-payer bill this year. The measure passed the state Senate but stalled in the Assembly, despite complete Democratic control in Sacramento, the capital.

The resistance from Pelosi and other Democratic leaders is tactical, not ideological. It took decades to pass something like Obamacare, and their concern is that, despite what polls might suggest, something as aggressive as single-payer just isn't politically feasible right now.

In fact, the congressional leaders you hear talking about single-payer are often Republicans, not Democrats. House Speaker Paul Ryan and other Republicans regularly float it as a worst-case Democratic alternative.

"Ultimately it's very clear that they're more interested in a single-payer system, which means government-run health care," Ryan said during the Senate push to repeal Obamacare. "Government-run health care is not in our nation's interest."

Senate Republicans even forced a vote on a single-payer option on the Senate floor last month, hoping to get Democrats on the record supporting the idea.

Most Democratic senators voted "present." No one voted "yes."

"I urged my colleagues to vote 'present' because we are not going to dance to the tune of right-wing Republicans, who of course were not prepared to support a single-payer," Sanders said. "For them, it was just a political moment that they thought would be advantageous for them."

Polls show single-payer is gaining support. A recent Pew Research survey showed the number of respondents favoring government-run health care has gone up percentage points this year alone and is 12 points higher than it was in 2014.

In a more important metric, more than half of House Democrats signed on to co-sponsor a single-payer bill earlier this year.

Jeff Weaver, a longtime adviser to Sanders, argues Democrats should be more aggressive on health care after a stretch during which broad swaths of voters organized against the GOP's Obamacare repeal effort. "This is a very powerful issue, in that people are prepared to be mobilized in support of their health care," Weaver said.

Like Sanders readily admits, this bill isn't going anywhere any time soon.

The whole thing is more about political framing — getting Democrats to the point where this would be a top priority whenever the party is back in power.

That is how progressive activists like Adam Green, the co-founder of the Progressive Change Campaign Committee, are viewing Sanders' impending bill rollout.

"If we left this debate with 20 senators on the record supporting single-payer, and the entire Senate Democratic caucus uniting around giving every American the option of buying into Medicare if they want to, that would be a wonderful place to land," Green said.